One of the newer variable speed drives for coupling a motor to a load which, for example, may be a pump is an apparatus called a hydroviscous disc pack. The hydroviscous disc pack has an input shaft which terminates in a plurality of closely-spaced discs. The output shaft originates in a plurality of closely-spaced discs which are positioned between the input shaft discs. In between the discs is provided an oil film. The oil film generates the sheer as the discs rotate, the sheer transmitting a force to the output disc, causing the discs to rotate. The disc pack consists of alternate hardened steel and friction discs that are splined so they are free to slide axially, relative to each other. Torque transmitted through the pack on input to output shaft depends on how much clamping force is exerted by a piston assembly pneumatically or hydraulically actuated. The servocontrolled valve suitably connected operates the clamping piston to vary its pressure on the stack of discs, hence, the torque transmitted to the load. Such a disc pack is described in the journal titled Product Engineering, Dec. 15, 1969, on pages 102 through 104.